This invention relates in general to antifriction bearings and, more particularly, to composite races for antifriction bearings and a process for manufacturing those races.
The races of a typical antifriction bearing are wrought steel throughout, and are derived from intermediate products such as high quality alloy steel tubes and bars which are quite expensive in their own right due to special processing used to produce them and the presence of scarce alloying components, such as nickel, chromium, and molybdenum, in them. The intermediate products are obtained only after a complex and expensive processing under special conditions of cleanliness. That processing basically involves producing a high alloy melt in an electric furnace, casting the melt into ingots, reheating, rolling into blooms, reheating, rolling into billets, then forging the billets or piercing them, and finally annealing.
A multitude of machining and heat treating processes are employed to convert the tubes or bars into bearing races, and these processes also add significantly to the cost of the bearing. This is particularly true in the case of tapered roller bearings which have flanged inner races (cones) and outer races (cups) that are somewhat more complex in terms of configuration than their counterparts in other types of antifriction bearings.
Two processes are currently employed to convert tubes or bars into the cups and cones for tapered roller bearings, at least on a large scale commercial basis. The first, which has probably experienced the greatest use, involves machining a section derived from a tube or a forging derived from a bar or tube to the size and shape desired for the race, then carburizing the machined configuration to case harden the steel if desired, next heat treating to provide the steel with the desired mechanical properties, and finally finish grinding to give the races their final form and size. In this procedure, large amounts of expensive alloy steel are lost as chips during the machining. Also, considerable energy is expended in the hot tube and bar-forming operations, as well as in the heat treatments and carburizing. The second process involves cold or hot forging cut steel bar slugs to a tubular shape corresponding generally to the desired shape of the race, then rough machining, next case carburizing, then heat treating, and finally finish grinding. While this process produces fewer chips, it still consumes a considerable amount of energy during forming and in the various heat treatments and grinds, and furthermore requires expensive forming dies.